The correct answer for which excerpts does not develop through the narrator's mental activity is “I trembled at the sound of my own voice . . . .”
The narrator mental activity can be distinguished from others excerpts because the narration from his own mind comes from the first person point of view while in this excerpt “I trembled at the sound of my own voice . . . .” is descriptive, it informs about how he felt rather than what he thought about this moment.